The present invention relates to a process for continuous production of polycarbonates and more particularly to the two-phase interface method.
A process for the production of polycarbonate is disclosed. The process, representing an improvement over the known interfacial polycondensation process entails introducing into the loop of a circulating reactor that additionally contains, a residence tank, an optional mixer, a pump, and a heat exchanger (i) an organic phase that contains a solvent for polycarbonate and phosgene and (ii) an aqueous phase that contains an aqueous lye solution, a dihydroxy compound and an optional monophenol to form an emulsion. Maintaining specified temperature and process conditions results in polycarbonate resin having good properties and in waste water that are characterized by their purity.
The two-phase interface process has been successfully used for many years in the production of polycarbonates. The process permits production of thermoplastic polycarbonates for a range of application areas, such as data carriers (CD, DVD), optical applications or medical applications.
Good heat stability and minimal yellowing are often described as important qualities of the polycarbonate. Less attention has hitherto been paid to the quality of waste water created during polycarbonate production. The contamination of waste water with residual organic materials, such as residual phenols, is of particular importance when considering the further treatment of waste water, for example by a waste treatment plant or by ozonolysis, to oxidize the residual organic materials. There have however been a number of applications in which methods for subsequent waste water treatment with the aim of reducing the content of phenolic components are predominantly describedxe2x80x94see, for example: JP 08 245 780 A (Idemitsu); DE 19 510 063 A1 (Bayer); JP 03 292 340 A (Teijin); JP 03 292 341 A (Teijin); JP 02 147 628 A (Teijin).
The contamination of waste water with residual organic materials, for example with bisphenols or phenols, may be kept to a minimum if a large excess of phosgene is used. However, this is not desirable for economic reasons.
When producing polycarbonates with reduced excess phosgene there is the risk that the bisphenol or the monophenol will not all react fully and will contaminate the waste water. There is the further risk that interface-active phenolic OH groups remaining in the polymer will complicate phase separation and washing. Consequently water-soluble impurities may not all be extracted from the organic phase. This may, in turn, adversely affect the quality of the product.
It is maintained that the production of high-quality polycarbonates by a continuous two-phase interface process and simultaneous low contamination of waste water was possible either only with considerable excess phosgene (uneconomical) or with phase separation problemsxe2x80x94along with loss in quality of the polycarbonatexe2x80x94or by subsequent treatment of the waste water.
The Applicant""s DE-A 42 27 372, disclosed the presently relevant arrangement of apparatus for the process according to the invention. In contrast to the teaching of the invention, however, no teaching may be inferred from DE-A 42 27 372 about the quantities and, in particular, the circulating conditions in which the educts are to be combined, let alone the fact that a particularly low content of residual organic materials, such as phenols and bisphenols, in waste water may be achieved by specially adjusted proportions and circulating conditions.
Starting from DE-A 42 27 372 the object is therefore to provide a process for producing high-quality products at the same time as a low content of organic materials in the waste water.
It has now surprisingly been found that very high-quality polycarbonate, measured by the yellowness index and by the terminal phenolic OH group content, is obtained in a continuous process, the process resulting in only low concentration of residual organic materials (residual phenols) in its waste water. In the process, a circulating reactor and at least one tubular reactor that is connected downstream thereof are used as reactor arrangement. Also critical are the specified reaction conditions and the ratio of added starting components to the quantity of circulated reaction emulsion.
A circulating reactor includes a circulating loop, a pump for circulating the reaction emulsion, a heat exchanger and a residence tank. The residence tank is equipped with means for continuous removal of part of the emulsion. The feeding points for the organic phase and the aqueous phase are situated between the residence tank and the pump. In embodiments where an optional mixer is used, these feeding points may be at the mixer.
The xe2x80x9ccirculating reactorxe2x80x9d is also shown schematically for the purpose of better understanding: 
The tubular reactor includes mixing and residence zones and is connected down-stream of the residence tank.
A key feature of the inventive process is the relative purity of the waste water:
The water is characterized in that it contains only low concentration of residual organic materials (residual phenols).
The process is an improvement of the well know two-phase interface process where polycarbonate is prepared from diphenols, phosgene, chain terminators, catalyst and optionally branching agents in a mixture of aqueous/alkaline phase and organic solvent phase. The process entails
(a) introducing into the circulating loop of a circulating reactor that additionally contains, in sequence a residence tank, an optional mixer, a pump, and a heat exchanger, through at least one point downstream from the residence tank and up stream from said pump,
(i) an organic phase that contains a solvent for polycarbonate and phosgene and
(ii) an aqueous phase that contains an aqueous lye solution, a dihydroxy compound and an optional monophenol to form an emulsion, wherein the temperature throughout the reactor is lower than 60, preferably 55xc2x0 C. to 25xc2x0 C., and wherein residence time of the emulsion in the circulating reactor is at least 2, preferably 2 to 15 minutes and
(b) removing from the residence tank a portion of the emulsion and pumping said portion into at least one tubular reactor equipped with at least one mixing zone and at least one residence zone and subjecting said portion to total residence time of 2 to 40 preferably 2 to 30 minutes in the tubular reactor,
with the provisos that
(aa) the rate at which the total amount of aqueous and organic phases is introduced in (i) relate to the flow rate of the emulsion as 1:3 to 1:12 preferably 1:3 to 1:10 and that
(bb) the rate of removal of the portion in (b) corresponds to said rate of introduction, and that
(cc) the molar amount of phosgene introduced to the reaction relates to the theoretical amount that is needed for the reaction of phosgene with dihydroxy compounds and with the optional monophenols as 1.12/1 to 1.22/1, preferably 1.14/1 to 1.20, and that
(dd) lye in an amount of 15 to 40 preferably 20 to 35 percent relative to the total weight of lye used in the process according to dd) and ee) is introduced into the circulating loop, and that
(ee) lye in an amount of 85 to 60, preferably 80 to 65 percent relative to the total weight of lye used in the process according to dd) and ee) is introduced into said portion of the emulsion, and that
(ff) monophenol chain terminator is optionally added into said portion, and that
(gg) catalyst is added to the said portion after residence time of 1 to 20, preferably 1 to 15 minutes of said portion in the tubular reactor.
xe2x80x9cDownstreamxe2x80x9d and xe2x80x9cupstreamxe2x80x9d are always taken to mean in the flow direction of the emulsion inside the circulating reactor in the present context.
The content of the phenolic component of the untreated waste water of the reaction is less than 100 ppm, preferably less than 50 ppm, particularly preferably less than 20 ppm.
Suitable diphenols are those of formula HOxe2x80x94Zxe2x80x94OH, in which Z is an aromatic radical with 6 to 45 C atoms, which may contain one or more aromatic nuclei, may be substituted and may contain aliphatic radicals or cycloaliphatic radicals or heteroatoms as bridging elements.
Examples are
dihydroxydiphenyls,
bis-(hydroxyphenyl)-alkanes
bis-(hydroxyphenyl)-cycloalkanes
bis-(hydroxyphenyl)-sulphides
bis-(hydroxyphenyl)-ethers
and the compounds thereof, which are alkylated and halogenated in the nucleus.
These and other suitable diphenols are described, for example, in U.S. Pat. Ser. Nos. 3,028,365, 4,982,014, 2,999,835, 3,148,172, 3,275,601, 2,991,273, 3,271,367, 3,062,781, 2,970,131 and 2,999,846, in DE-A 15 70 703, 20 63 050, 20 63 052, 22 11 956, the French patent specification 1 561 518 and in DE-A 38 33 953.
Preferred diphenols are:
2,2-bis-(4-hydroxyphenyl)-propane (Bisphenol-A) and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethyl-cyclohexane (TMC-bisphenol).
It is emphasized here that the process according to the invention may be used for virtually all diphenols.
In the process according to the invention the diphenols are used in aqueous alkaline solution, the concentration of diphenols being 10 to 20%, preferably 12.5 to 17.5%, the quantity of alkali being 1.0 to 3.0 mol lye per mol bisphenol and being dependent on the solubility of the bisphenol used.
The phosgene is used in organic solvents in a concentration of 7 to 10%, preferably 8 to 9.5%
Suitable chain terminators and branching agents are known. Examples of suitable chain terminators are disclosed in DE-A 38 33 953. Preferred chain terminators are phenol, cumylphenol, isooctylphenol, para-tert.-butylphenol. The chain terminators may be added neat or in various concentrations as a solution in organic solvents.
Preferred branching agents are trisphenols and tetraphenols and 3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindol. The branching agents may also be added neat or in various concentrations as a solution in organic solvents.
Sodium hydroxide solution or potassium hydroxide solution are used as lye, and alkaline-earth lyes may optionally also be used. Aqueous sodium hydroxide solution is preferred. The concentration of the NaOH in the aqueous sodium hydroxide solution corresponds to that of commercially available lyes, in other words between 20 and 60%, preferably between 30 and 50%, most particularly preferred is sodium hydroxide solution obtained directly from the amalgam or diaphragm process of the chlorine-alkali electrolysis at concentrations of about 50 or 32% respectively.
All percentages in the present context are taken to mean wt. % unless explicitly stated otherwise.
In principle, any catalysts known for producing polycarbonates by the two-phase interface process, such as tert.amines, may be used as catalysts. N-ethyl-piperidine and triethylamine are preferred.
The organic phase contains solvents or a solvent mixture which dissolves polycarbonate. Suitable solvents are any known solvents which are capable of dissolving the polycarbonate to at least 5 wt. % at temperatures of about 20xc2x0 C., and mixtures thereof.
Methylene chloride, toluene, monochlorobenzene are preferred, methylene chloride and mixtures of methylene chloride and monochlorobenzene in a ratio of 20:80 parts by weight to 75:25 parts by weight being particularly preferred.
A pH between 9 and 14, preferably between 9.5 and 13.0, is adjusted throughout the reaction. This is effected in that the quantity of lye required to dissolve the diphenols is introduced once at the start, then the lye is first subsequently added upstream of the heat exchanger and is subsequently added upstream of the tubular reactors, optionally together with the chain terminator.
The polycarbonates may be processed in a known manner to form any molded articles, and additives, such as stabilizers, mold-release agents or flame retardants, fillers or glass fibers, conventional in thermoplastic polycarbonates, may be added before or during processing.
The polycarbonates obtained by the process according to the invention may be used industrially in a known manner as any molded articles or even sheets and films, for example in the automotive industry or in optical applications, optical and magneto-optical storage media.
The following applications are mentioned by way of example but without being limiting:
1. Safety screens, required, as is well known, in many areas of buildings, vehicles and aeroplanes, and as helmet visors.
2. Producing foils, in particular ski foils.
3. Producing blown articles (see for example U.S. Pat. No. 2,964,794), for example 1 to 5 gallon water bottles.
4. Producing light-permeable panels, in particular hollow chamber panels, for example for covering buildings such as railway stations, glass houses and lighting installations.
5. Producing optical data memories.
6. For producing traffic light casings or traffic signs.
7. For producing foamed materials (see for example DE-B 1 031 507).
8. For producing filaments and wires (see for example DE-B 1137 167 and DE-A 1 785 137).
9. As translucent plastics materials with a glass fiber content for lighting engineering purposes (see for example DE-A 1 554 020).
10. As translucent plastics materials with a barium sulphate, titanium dioxide and/or zirconium oxide content or organic polymeric acrylate rubbers (EP-A 634 445, EP-A 269 324) for producing light-permeable and light-scattering molded parts.
11. For producing precision injection molded particles, such as lens holders. For this purpose polycarbonate with a glass fiber content, optionally additionally containing about 1 to 10 wt. % MoS2, based on the total weight, is used.
12. For producing optical apparatus components, in particular lenses for photo-cameras and film cameras (see for example DE-A 2 701 173).
13. As light transmission carriers, in particular as optical fiber cables (see for example EP-A1 0 089 801).
14. As electric insulating materials for electric conductors and for connector casings and connectors.
15. Production of mobile phone casings with improved resistance to perfume, aftershave and perspiration.
16. Network interface devices.
17. As carrier materials for organic photoconductors.
18. For producing lights, for example headlights, as so-called head-lamps, light scattering discs or inner lenses.
19. For medical applications, for example oxygenators, dialysers.
20. For foodstuff applications, such as bottles, kitchenware and chocolate molds.
21. For applications in the automotive sector, where contact with fuels and lubricants can occur, such as bumpers, optionally in the form of suitable blends with A-BS or suitable rubbers.
22. For sports articles, such as slalom poles or ski boot bindings.
23. For household articles, such as kitchen sinks and letterbox casings.
24. For housings, such as distribution cabinets.
25. Casings for electric toothbrushes and hairdryers.
26. Transparent washing mach in e portholes with improved resistance to the washing solution.
27. Safety glasses, optical correcting glasses.
28. Light coverings for kitchen appliances with improved resistance to kitchen vapour, in particular oil vapors.
29. Packaging films for pharmaceutical preparations.
30. Chip boxes and chip carriers.
31. For other applications, such as barn doors or animal cages.
The following examples are intended to illustrate the present invention without, however, limiting it thereto.